Ball joints generally comprise a stud which includes a shank and a ball end, and a housing in which the ball end is seated. The ball joint permits the ball end and shank to rotate about the stud axis, as well as to swing or pivot with respect to the stud axis. The housing usually contains a pair of bearing seat members. The bearing seat members have spherical surfaces, and are positioned within the housing in axially opposed relationship to provide bearing surfaces against which the surface of the ball end can slide. A spring biases one of the bearing seat members against the ball end to hold the ball end firmly between the bearing seat members.
The housings of such ball joints vary in form. Solid unitary housings are known which are machined forgings or castings. Also, housings are known which are formed from one or more stamped metal pieces. For example, U.S. Pat. No. 3,259,408 to Herbenar shows a ball joint with a unitary solid housing. A lubricant is sealed within the housing by means of a plug at one end of the housing, and a boot seal extends between the stud shank and the other end of the housing.
U.S. Pat. No. 2,420,621 to Ricks shows a ball joint housing formed from a piece of sheet metal stamped into a cup shape. The cup-shaped housing is clinched or spun into a spherical shape to enclose the bearing seat members by folding sections of the housing across an open slot in the sheet metal material. This type of housing suffers from the disadvantage of having a seam through which a lubricant could leak at the closed slot.
Another type of ball joint is shown in U.S. Pat. No. 1,898,100 to Skillman wherein a housing is formed from a stamped sheet metal piece having two sections. The two sections are pivoted about a fold line to bring cup-shaped portions of the two sections into overlying relationship. The overlying cup-shaped portions of the housing define a chamber for the ball end of the stud. A seam extends around the chamber between the overlying edges of the cup-shaped portions. This type of housing structure also suffers from the disadvantage of having a seam through which a liquid lubricant could leak. Furthermore, stamped sheet metal structures are generally not as strong as solid forgings or castings.